For centuries asphalt and other bituminous products have been used to provide waterproofing and protective coverings and coatings for roofs, foundations, and the like; resilient, weather resistant pavings; and sealants useful in a wide variety of applications. Long ago it was found that the undesirably low melting or softening points of natural asphalts could be raised through the addition of oxygen, and that that advantage and others offered by oxidized asphalt could be extended through the use of rubber or other polymer modifiers. Raising the softening point of an asphalt improves its performance in applications subject to moderately warm or hot temperatures, such as for example roofing--on a typical sunny summer day, for example, the temperature of a black asphalt roof may easily reach temperatures in excess of 125.degree. F. As the softening point of a straight unoxidized asphalt (that is, an asphalt taken straight from the petroleum refining process or from a natural bitumen deposit) is typically about 70.degree. F., such temperatures can cause sagging or running in the asphalt, resulting in a loss fluid-tight or sealing integrity of the roof and a diminishment or complete abrogation of its value as a sealing barrier.
Oxidized or "air blown" asphalts, however, have not been useable in many applications. For example, among the most important classes of asphalt products are emulsified coatings, sealants, adhesives, and mastics capable of being applied at typical ambient temperatures (between about 35.degree. F. and about 120.degree. F.). Such emulsions are used both for the construction of primary sealing and waterproofing membranes and for patching and repair of existing membranes. But it has proven particularly difficult to reliably and economically emulsify oxidized asphalts for use as coatings, sealants, adhesives, and mastics applied at ambient temperatures. Emulsified asphalts are typically made by processing non-oxidized straight run or "flux" asphalts in high shear milling machines with slurries comprising water and soaps such as bentonite clays or other chemical catalysts. When this is tried with oxidized asphalts (such as for example any ASTM D312 oxidized asphalts) the emulsion process fails: the asphalt and slurry fail to combine. Typically the asphalt is so viscous, due to its elevated softening point, that the milling machine is incapable of maintaining operational RPMs and bogs down. Thus despite the clear superiority of oxidized asphalts in almost all applications, including emulsions, it has not been possible to produce oxidized asphalt emulsion products. The same is true with respect to oxidized asphalts modified by the addition of rubber and other polymers, which are known to possess superior weather-resistance, resistance to ultraviolet (UV) rays and ozone, resistance to thermal shock cycles (i.e. thermal stress cycles induced by, for example, daily exposure to cycles of warm sun and cool darkness), and durability under impacts, etc.
Typical of the machinery used for making non-oxidized asphaltic emulsions until the advent of the invention disclosed herein is the prior art mill shown schematically in FIG. 1. Prior art mill 1 comprises rotor 12 with blades 13 housed in a mixing chamber formed by the inner surface of casing 14. Non-oxidized asphalt is fed into the mixing chamber through line 10 and blended with slurry fed through line 11. After mixing, emulsified product is removed via line 17. A typical mill comprises two or more rows of blades 13, which are often made of simple blunt cylindrical objects such as bolts. Typical geometry provides a rotor radius 15 of approximately 7 to 8 inches and a grinding gap or minimum clearance of two or more inches. With a rotor speed of 1200 RPM and a rotor power input of approximately 10 horsepower, such a mill can produce about 90 to about 120 gallons per minute of non-oxidized asphaltic emulsion. When the use of oxidized asphalt was attempted, machines of this type bogged down and failed to properly emulsify the asphalt.
Many attempts have been made to improve the various characteristics of emulsified asphalts, but none have addressed the problem of making them with oxidized asphalt bases. For example, U.S. Pat. Nos. 5,558,702, 5,667,577, and 5,667,576 to Chatterjee et al.; 5,711,796 to Grzybowski et al.; and 4,822,247 4,985,079 to Graf et al. describe various improvements in asphaltic emulsions. But none teaches or suggests a method of providing such emulsions with the advantages of the elevated softening point of an oxidized asphalt base, or of doing so with the added benefits offered by modification of the base asphalt by rubber or other polymers. The Gryzbowski reference discusses oxidization products of naturally occurring asphalts from the Orinoco belt of Venezuela, made partially with the use of water, but the water is ultimately removed from the product and is introduced solely for the purpose of aiding oxidation of the particular asphalts described. The oxidation of straight or flux asphalt is, in general, a relatively well-understood problem; the problem arises upon attempting to emulsify such asphalts.
Thus there exists a need for an asphaltic emulsion that is suitable for use as a roofing, waterproofing, and sealing compound and which enjoys the benefits of a fully oxidized asphalt base. There is also a need for an effective, efficient, economical method for making such an emulsion. There is a further need for such emulsions made with rubber or other polymer-modified asphalt bases, and for methods for making such modified emulsions.